Polyethylene resins and its compounds for container uses and containers

ABSTRACT

The present invention provides polyethylene resin and its compounds for container uses, which realize molding of thin-walled articles and high-speed molding, achieves/achieve excellent printability and stress cracking resistance and are suitable for container uses involving tubes, bottles, etc., and containers. Specifically, there are provided a polyethylene resin compound for container uses comprising linear polyethylene having a narrow molecular weight distribution and satisfying specific properties and containers produced therefrom.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/JP99/02035 which has an Internationalfiling date of Apr. 16, 1999, which designated the United States ofAmerica.

TECHNICAL FIELD

The present invention relates to polyethylene resin and its compoundsfor container uses, and containers. More specifically, the presentinvention relates to polyethylene resin or its compounds which realizemolding of thin-walled articles and high-speed molding, achieves/achieveexcellent printability and stress cracking resistance and are suitablefor container uses involving tubes, bottles, etc. and containers.

BACKGROUND ART

Containers such as tubes for cosmetics, shampoo and detergent, foodpackaging tubes for mayonnaise, etc., and food packaging bottles for soysauce, etc. usually have small wall thickness and are manufactured inthe blow molding method. These containers are constructed of, forexample, either a single layer of high-pressure low-densitypolyethylene, or two layers consisting of a high-pressure low-densitypolyethylene layer and a high-density polyethylene layer. The aforesaidcontainer is required to have excellent properties such as environmentalstress cracking resistance (ESCR), printability, etc.

The recent trend has been such that improvement in the productivity ofthese tubes was strongly desired. In order to achieve the improvement inthe productivity, studies have been made on approaches to high-speedtube forming processes using linear low-density polyethylene (L-LDPE).Although use of the linear low-density polyethylene of the conventionaltype certainly facilitates tube forming at high speed, this approach isaccompanied by such problem that printing is totally hampered due to thebleeding phenomenon caused by the solvent used in printing ink duringthe process of printing executed on the surface of the tube.

Such being the case, circles interested have been looking forward to anintroduction of such polyethylene resin or its compounds thatrealizes/realize molding of thin-walled articles and high speed molding,achieves/achieve excellent printability and stress cracking resistanceand is/are suitable for container uses involving tubes, bottles, etc.

The present invention is intended to resolve the aforesaid problemsassociated with the conventional technology, and it does provide suchpolyethylene resin and its compounds that realize molding of thin-walledarticles and high speed molding, achieve excellent printability andstress cracking resistance, and are suitable for container usesinvolving tubes, bottles, etc., and containers.

DISCLOSURE OF THE INVENTION

Polyethylene resin and its compounds of the present invention comprise apolyethylene resin and resin compounds for container uses, that achievea 50% cracking appearance time (F₅₀) (the elapsed time when 50% ofspecimens fail), which is an index of stress cracking resistance, of 100or more hrs. and demonstrate the characteristic of being substantiallyfree of any peel area (the area of defect loss part) on the printedsurface in a squared cut test performed on film produced therefrom.

The polyethylene resin for container uses of the present inventionrepresents a polyethylene resin and resin compounds comprising linearpolyethylene (A) satisfying the following requirements,

(i) Molecular weight distribution (Mw/Mn) as determined by GPC is 2-3.5,

(ii) Density is 0.890-0.975 g/cm³, and

(iii) Content of component soluble in n-decane at room temperature is 2%by weight or less;

which achieves a 50% cracking appearance time (F₅₀) of 100 or more hrs.and demonstrates the characteristics of being substantially free of anypeel area on the printed surface in a squared cut test performed on filmproduced therefrom.

The polyethylene resin and its compounds for container uses,respectively, of the present invention achieves/achieve a 50% crackingappearance time (F₅₀), which is an index of stress cracking resistance,of 100 or mores hrs.

The polyethylene resin and its compounds for container uses, of thepresent invention are required to have such excellent stress crackingresistance as described above and, at the same time, achieve suchexcellent printability that the printed surface does not substantiallyget peeled off in a squared cut test performed on film produced fromsaid polyethylene resin and its compounds.

While a detailed explanation is furnished afterwards about the squaredcut test, the phrase “does not substantially get peeled off” means that90% or more, or preferably 95% or more, of coated sections on a specimenfilm tested in the squared cut test does not get peeled off.

So long as all of the aforesaid requirements are satisfied, thepolyethylene resin and its compounds of the present invention can besuitably utilized as resins for container uses.

The linear polyethylene (A) of the present invention comprises a linearpolyethylene which satisfies the following requirements.

(i) Molecular weight distribution (Mw/Mn) as determined by GPC is 2-3.5,

(ii) Density is 0.890-0.975 g/cm³, and

(iii) Content of component soluble in n-decane at room temperature is 2%by weight or less.

The molecular weight distribution is within the range of 2-3.5, orpreferably 2-3. When linear polyethylene (A) whose molecular weightdistribution is in the aforesaid range is used, there can be providedcontainers having excellent environmental stress cracking resistance(ESCR) and printability. The molecular weight distribution as referredto in the present invention means molecular weight distribution (Mw/Mn)wherein “Mw” is weight average molecular weight and “Mn” is numberaverage molecular weight as determined by GPC in accordance with atesting procedure described hereinafter.

The linear polyethylene (A) of the present invention comprisesethylene-α-olefin copolymer obtained by copolymerizing ethylene withα-olefin having 3-20 carbon atoms.

As specific examples of said α-olefin, there can be cited α-olefinshaving 3-20 carbon atoms such as propylene, 1-butene, 1-pentene,1-hexene, 4-methyl-1-pentene, and 1-octene. Preferred ones among theaforesaid α-olefins are α-olefins having 3-8 carbon atoms such as1-hexene, 4-methyle-1-pentene, and 1-octene.

The linear polyethylene (A) as used in the present invention containsthe structural unit derived from ethylene of usually 95-99 mol. %,preferably 96-98 mol. %, and the structural unit derived from α-olefinhaving 3-20 carbon atoms at a mol. ratio of usually 1-5 mol. %,preferably 2-4 mol. %.

This linear polyethylene (A) has a density of 0.890-0.975 g/cm³,preferably 0.900-0.960 g/cm³, more preferably 0.900-0.950 g/cm³,furthermore preferably 0.910-0.930 g/cm³. When linear polyethylene (A)of a density falling in said ranges is used, there can be providedcontainers having excellent environmental stress cracking resistance(ESCR) and printability.

The liner polyethylene (A) as used in the present invention contains 2%by weight or less of component soluble in n-decane at room temperature,or preferably 1% by weight or less. When linear polyethylene (A)containing 2% by weight or less of solubles in n-decane at roomtemperature is used, there can be provided containers having excellentprintability. The less component soluble in n-decane at room temperatureare, the narrower becomes the composition distribution.

It is preferable that the linear polyethylene (A) of the presentinvention satisfies the following relationship between the melt tension(MT) (g) at a temperature of 190° C. and the melt flow rate (MFR)(g/10min.).

MT>2.2×MFR^(−0.84)  (i)

It is preferable that the linear polyethylene (A) of the presentinvention satisfies the following relationship between the quantity ofcomponent soluble in decane at room temperature (W)(% by weight) and thedensity (d)(g/cm³).

 When MFR≦10 g/10 min., W<80×exp(−100(d−0.88))+0.1  (ii-a)

When MFR>10 g/10 min., W<80×(MFR−9)^(0.26)×exp(−100(d−0.88))+0.1  (ii-b)

It is preferable that the linear polyethylene (A) of the presentinvention satisfies the following relationship between the highest peak(Tm)(° C.) in the endothermic curve as determined using differentialscanning calorimeter (DSC) and the density (d).

Tm<400d−248  (iii)

It is most preferable that the linear polyethylene (A) of the presentinvention satisfies the aforesaid relationships (i), (ii-a) or (ii-b),and (iii) altogether.

It is furthermore preferable that the linear polyethylene (A) of thepresent invention satisfies the following relationship between thefluidity index (FI)(1/sec) which is defined by the shear rate when theshear stress of the molten polymer at a temperature of 190° C. reaches2.4×10⁶ dyne/cm² and the melt flow rate (MFR)(g/10 min.).

FI>75×MFR  (iv)

By the way, the melt flow rate of the linear polyethylene (A) is in therange of 0.1-300 g/10 min., or preferably 0.1-100 g/10 min., or morepreferably 0.2-10 g/10 min.

Among all types of linear polyethylene (A) achieving the aforesaidproperties, a particularly preferred one for the purpose of the presentinvention is ethylene-α-olefin copolymer obtained by copolymerizingethylene with α-olefin having 3-12 carbon atoms in the presence of anolefin polymerization catalyst containing a metallocene catalystcomponent (a).

The linear polyethylene (A) of the metallocene catalyst type asdescribed above can be manufactured by copolymerizing ethylene withα-olefin having 3-20 carbon atoms in the presence of an olefinpolymerization catalyst, which is referred to as “metallocene-typeolefin polymerization catalyst” containing a metallocene catalystcomponent such as the ones disclosed in Japan Laid-open PatentApplication 1994-9724, Japan Laid-open Patent Application 1994-136195,Japan Laid-open Patent Application 1994-136196, and Japan Laid-openPatent Application 1994-207057.

This kind of metallocene-type catalyst generally comprises a metallocenecatalyst component comprising a compound of transition metal belongingto Group IVB of Periodic Table having at least one ligand of thecyclopentadienyl skeleton (a1), an organo-aluminum oxy compound catalystcomponent (b), a fine particulate carrier (c) and, as required, anorgano-aluminum compound catalyst component (d) and/or an ionizationionic compound catalyst component (e).

As a metallocene catalyst component preferably used in the presentinvention (al), there is a compound of transition metal belonging toGroup IVB of Periodic Table having at least one ligand of thecyclopentadienyl skeleton. There can be cited as an example of this kindof transition metal compound such transition metal compound as isrepresented by the following formula [I].

ML¹ _(x)  [I]

wherein x is the valency of transition metal atom M.

M is the transition metal atom selected from among those belonging toGroup IVB of Periodic Table. Specifically, they are zirconium, titanium,and hafnium. The preferred one among these is zirconium.

L¹ is the ligand coordinated in transition metal atom M. At least oneligand L¹ is of the type having the cyclopentadienyl skeleton.

As the ligand L¹ having the cyclopentadienyl skeleton which iscoordinated in the transition metal atom M as described above, there canbe specifically cited alkyl-substituted cyclopentadienyl group such ascyclopentadienyl; indenyl group; 4,5,6,7-tetrahydroindenyl group; andfluorenyl group. These groups may be substituted with halogen atom,trialkylsilyl group, etc.

In cases where the compound represented by the above-cited formula [I]contains two or more groups of the cyclopentadienyl structure, twocyclopentadienyl structure groups among them may be bonded to each othervia an alkylene group such as ethylene and propylene; silylene group orsubstituted silylene group such as dimethylsilylene group,diphenylsilylene group, methylphenyl silylene group, etc.

There may be preferably used alumoxane as the organo-aluminum oxycompound catalyst component (b). Specifically, there are employedmethylalumoxane, ethyl alumoxane, methylethyl alumoxane, etc. havingusually 3-50 repeat units represented by the following formula.

—Al(R)O—

wherein R is an alkyl group.

The fine particulate carrier (c) employed for preparing the olefinpolymerization catalyst (c) is either an inorganic or organic compound,either in the granular solid or in a fine particulate solid whoseparticle diameter is generally 10-300 μm, or preferably 20-200 μm.

A porous oxide is preferred as the inorganic carrier. Specifically,SiO₂, Al₂O₃, MgO, ZrO₂, TiO₂, etc. can be exemplified.

As specific examples of organo-aluminum compound catalyst component (d)which is employed, as required, in the preparation of the olefinpolymerization catalyst, there can be cited trialkyl aluminum such astrimethyl aluminum; dialkyl aluminum halide such as dimethyl aluminumchloride; alkyl aluminum sesquehalide such as methylaluminumsesquechloride.

As examples of the ionization ionic compound catalyst component (e),there can be cited Lewis acid such as triphenyl boron described in U.S.Pat. No. 5,321,106, MgCl₂, Al₂O₃, and SiO₂—Al₂O₃; ionic compound such astriphenylcarbenium tetrakis(pentafluorophenyl) borate; carboranecompounds such as dodecaborane, bis-n-butyl ammonium (1-carbedodeca)borate.

The linear polyethylene (A) used in the present invention can beobtained by copolymerizing ethylene with α-olefin having 3-20 carbonatoms in the gas phase, or in the liquid phase such as the slurry stateor the solution satate under various conditions in the presence of theaforesaid olefin polymerization catalyst.

For preferred linear polyethylene (A) used as the polyethylene resin orits compounds for container uses in the present invention, there can becited linear polyethylene (Al) within the preferred ranges of amolecular weight distribution (Mw/Mn) as determined by GPC of 2-3.5,preferably 2-3, a density of 0.900-0.950 g/cm3, preferably 0.905-0.930g/cm³, a content of component soluble in n-decane at room temperature of2% by weight or less, preferably 1% by weight or less, and a melt flowrate of 0.1-10 g/10 min., preferably 0.2 -10 g/10 min.

It is by using the linear polyethylene (Al) that the polyethylene resinfor container uses of the present invention can be obtained.

Furthermore, the polyethylene resin compound for container uses of thepresent invention is obtained by mixing the linear polyethylene (Al)with another resin. As an example of resins suitably useable as saidanother resin, high-pressure low-density polyethylene (B) may be cited.

Explanations are furnished as follows about a compound comprising linearpolyethylene (A1) and high-pressure low-density polyethylene (B) whichis cited as an example of the polyethylene resin for container uses ofthe present invention.

High-pressure low-density polyethylene (B), which may be used in thepolyethylene resin compound for container uses of the present inventio,is a polyethylene manufactured from ethylene under high-pressure in thepresence of a radical polymerization catalyst. As required, a smallamount of another vinyl monomer may be copolymerized.

The high-pressure low-density polyethylene (B) used in the presentinvention is in the range of 0.910-0.930 g/cm³, preferably 0.915-0.930g/cm³.

This high-pressure low-density polyethylene (B) has a melt flow rate of0.2-10 g/10 min., preferably 0.2-5 g/10 min., more preferably 0.3-3 g/10min. Use of high-pressure low-density polyethylene (B) having a meltflow rate whithin the aforesaid range facilitates high-speed molding ofcontainers.

Linear polyethylene (Al) is used by more than 50% to less than 100% byweight, or preferably more than 60% to less than 100% by weight, morepreferably more than 70% to less than 100% by weight based on 100% byweight representing the total weight of the linear polyethylene (Al) andthe high-pressure low-density polyethylene (B). Use of the linearpolyethylene (Al) having the aforesaid properties by said ratio can givea polyethylene resin or its compound, which can provide containershaving excellent environmental stress cracking resistance andprintability.

High-pressure low-density polyethylene (3) is used by not more than 50%to more than 0% by weight, preferably not more than 40% to more than 0%by weight, more preferably 10-30% by weight based on 100% by weightrepresenting the total weight of linear polyethylene (Al) andhigh-pressure low-density polyethylene (B). When high-pressurelow-density polyethylene (B) having the aforesaid properties is used bysaid ratio, the obtained polyethylene resin compound realizes stablehigh-speed molding of containers by virtue of its high melt tensionwhich restrains pulsation of the parison.

As another preferred mode of the linear polyethylene (A) used for otherpolyethylene resin compounds for container uses of the presentinvention, there can be cited linear polyethylene (A2). Linearpolyethylene (A2) has a molecular weight distribution (Mw/Mn) asdetermined by GPC of 2-3.5, preferably 2-3, a density of 0.890-0.920g/cm³, preferably 0.900-0.920 g/cm³, a content of component soluble inn-decane at room temperature of 2% by weight or less, preferably 1% byweight or less, and a melt flow rate of 0.1-5 g/10 min., preferably0.1-2 g/10 min.

Linear polyethylene (A2) can be suitably used particularly in the formof a compound prepared together with another resin.

As an example of another mode of use of the linear polyethylene (A)which can be suitably used in the form of a compound prepared togetherwith another resin, there can be furthermore cited linear polyethylene(A3).

Linear polyethylene (A3) has a molecular weight distribution (Mw/Mn) asdetermined by GPC of 2-3.5, preferably 2-3, a density of 0.920-0.975g/cm³, preferably 0.930-0.960 g/cm³, a quantity of component soluble inn-decane at room temperature of 2% by weight or less, preferably 1% byweight or less, and a melt flow rate of 5-300 g/10 min, preferably10-100 g/10 min.

The aforesaid linear polyethylene (A2) can be mixed with the aforesaidlinear polyethylene (A3) to obtain a polyethylene resin compound of thepresent invention. Moreover, a mixture of the linear polyethylene (A2)and/or the linear polyethylene (A3) with the aforesaid high-pressurelow-density polyethylene (B) can be a polyethylene resin compound forcontainer uses of the present invention.

That is to say, a compound comprising at least 2 kinds of resin selectedfrom among the linear polyethylene (A2), the linear polyethylene (A3)and the high-pressure low-density polyethylene (B) can be used as apolyethylene resin compound for container uses of the present invention.The linear polyethylene (A2) is used by 0-70% by weight, or preferably10-60% by weight, or more preferably 30-50% by weight based on 100% byweight representing the total weight of the linear polyethylene (A2),the linear polyethylene (A3) and the high-pressure low-densitypolyethylene (B). And, the linear polyethylene (A3) is used by 0-70% byweight, preferably 10-60% by weight, more preferably 20-40% by weightbased on 100% by weight representing the total weight. When the linearpolyethylene (A3) having the aforesaid properties is used by said ratio,there is obtained such polyethylene resin compound that can providecontainers having excellent environmental stress cracking resistance(ESCR) and printability.

The high-pressure low-density polyethylene (B) is used by 50-0% byweight, preferably 40-0% by weight, more preferably 10-30% by weightbased on 100% by weight representing the total weight of the linearpolyethylene (A2), the linear polyethylene (A3), and the high-pressurelow-density polyethylene (B). When the high-pressure low-densitypolyethylene (B) having the aforesaid properties is used by said ratio,the polyethylene resin compound thus obtained realizes stable molding ofcontainers at high speed by virtue of its high melt tension (MT) whichrestrains pulsation of the parison.

Amounts to be used of the linear polyethylene (A2), the linearpolyethylene (A3) and the high-pressure low-density polyethylene (B),respectively, are selected in such manner that the total becomes 100% byweight, from the above-cited ranges.

As actual modes of polyethylene resin compound containing the aforesaidlinear polyethylene (A2), linear polyethylene (A3) or high-pressure lowdensity polyethylene (B), there can be cited the following compounds.

(1) A compound comprising the linear polyethylene (A2) and the linearpolyethylene (A3);

(2) A compound comprising the linear polyethylene (A2) and thehigh-pressure low-density polyethylene (B); and

(3) A compound comprising the linear polyethylene (A2), the linearpolyethylene (A3) and high-pressure low-density polyethylene (B).

There may be compounded into the polyethylene resin or its compounds forcontainer uses, of the present invention, as requested, known heatstabilizer, UV stabilizer, pigment, antioxidant, antistatic agent, slipagent, filler, etc. to an extent not detrimental to the purpose of thepresent invention.

The polyethylene resin compound for container uses of the presentinvention can be obtained by means of mixing the aforesaid componentseither in a known method using, for example, Henschel mixer, V-blender,ribbon blender, tumbler blender, etc., or by means of furthermoremelt-kneading the thus obtained mixture using a single-screw extruder, adouble-screw extruder, a kneader, a Banbury mixer or the like, andthereupon by pelletizing the kneaded material or pulverizing the thusobtained lumpy resin.

From the polyethylene resin compound or polyethylene resin obtained bythe aforesaid method can be manufactured tubes for cosmetics, shampoo,and detergent, food packaging tubes for mayonnaise, etc., and foodpackaging bottles for soy sauce, etc. by the known extrusion blowmolding method.

Since the polyethylene resin and its compounds for container uses,respectively, of the present invention contain extremely low content ofthe component soluble in n-decane at room temperature and consequentlythe soluble component does not bleed into the interior of the containerwhen they are used as a resin for the internal layer of the container,they are suitable for the manufacture of food containers.

The polyethylene and its compounds resin for container uses of thepresent invention are suitable as a resin for the internal layer of thecontainer constructed of two or more layers for which the aforesaidproperties are exploited.

The properties cited in the present invention were determined inaccordance with the following test methods.

Test methods

(1) 50% Cracking Appearance Time (F₅₀) (Environmental Stress CrackingResistance (ESCR))

2-mm thick compression-molded test sheets were prepared in accordancewith ASTM D-1698. Stress cracking resistance tests were carried out withthose test sheets for determining a 50% cracking appearance time (F₅₀).For the purpose of the present invention, this 50% (F₅₀) was adopted asthe index of stress cracking resistance.

(2) Squared Cut Test (Adhesion of Printing Ink to the Film (Tube)

The film subjected to this squared cut test (0.4 mm thick) was formed inaccordance with the following procedure.

A tube was formed with a tube-molding machine under molding conditionsof a resin temperature of 200° C. and a tube take-up speed of 15 m/min.

After subjecting the surface of the thus obtained tube to a coronadischarge treatment under such condition that a wetting index of 38dyne/cm or more was achieved, screen-printing was carried out on thesurface of the tube using ultraviolet-curable type ink. The speed ofscreen-printing was 10 m/min.

Thereupon, a squared cut test was performed on this printed film inaccordance with the following procedure. The squared cut test wasperformed in accordance with JIS K-5400. That is to say, after immersingthe printed specimen in warm water maintained at a temperature of 40° C.for 10 minutes, 11 lines×11 lines with 1 mm intervals were cut into thesurface of the printed specimen to a depth equivalent to the thicknessof the coat. Next, a 100 mm-wide cellophane adhesive tape was stickedonto the cut surface, and the entire surface was rubbed with a rubbingstick in 10 reciprocating strokes in both the lengthwise and widthwisedirections. Finally, the cellophane adhesive tape was instantaneouslypeeled off from the front end.

The adhesion property of the coat was shown in terms of the number ofremaining sections of the coat (on average of 3 specimens tested).

(3) Molecular Weight Distribution (Mw/Mn)

Molecular weight distribution (Mw/Mn) was determined in accordance withthe following procedure using GPC-150C manufactured by Millipore Co.

The packed (separation) column was TSK GNH HT, and the column dimensionswere 72 mm in diameter×600 mm in length. The column temperature was setat 140° C. Using o-dicychlorobenzene (manufactured by Wako Junyaku KogyoK. K.) for the mobile phase and 0.025% by weight of BHT (manufactured byTakeda Chemical Industries, Ltd.) as antioxidant, the specimen was movedat a speed of 1.0 ml/min. The concentration of the specimen was 0.1% byweight and the volume of injected sample was 500 μL. As the detector,differential refractometer was used. As polystyrene standards, productsof Tosoh, Ltd. were used for the molecular weight ranges of less than1000, and more than 4×10⁶ and products of Pressure Chemical Co., Ltd.for the molecular weight ranges of more than 1000, but less than 4×10⁶.

(4) Composition of Polyethylene

The composition of linear polyethylene was determined by analyzing¹³C-NMR spectra of specimens obtained by dissolving about 200 mg oflinear polyethylene in 1 ml of hexachlorobutadiene in a test tube of 10mm diameter under the testing conditions of a 120° C. temperature, atest frequency of 25.05 MHz, a spectrum width of 1500 Hz, a pulse repeattime of 4.2 sec., and a pulse width of 6 μsec.

(5) Density

The density was determined in accordance with the procedures prescribedin ASTM D-1505. The density was determined with a density gradient tubeafter heat-treating a strand, which was obtained at the time ofmeasuring the melt flow rate (MFR) under a load of 2.16 kg at 190° C.,at 120° C. for 1 hr and gradually cooling it to the room temperature in1 hr.

(6) Quantity of Component Soluble in n-decane

The quantity of component soluble in n-decane contained in linearpolyethylene was determined in the following procedure. 3 g ofpolyethylene was added to 450 ml of n-decane to be dissolved at 145° C.After cooling the solution to 23° C., insolubles in n-decane wereremoved by filtration and solubles in n-decane were recovered from thefiltrate.

(7) Melt Flow Rate

The melt flow rate was determined in accordance with ASTM D-1238 at atemperature of 190° C. under a load of 2.16 kg.

(8) Melt Tension (MT)

The melt tension was determined by measuring the stress applied when themolten polyethylene was stretched at a constant rate. That is to say,the melt tension was determined using an MT tester manufactured byToyoseiki Seisakusho, Ltd. using polyethylene pellets as the testspecimen under testing conditions of a resin temperature of 190° C., anextrusion speed of 15 mm/min., a wind-up speed of 10-20 m/min., a nozzlediameter of 2.09 mm and a nozzle length of 8 mm.

EXAMPLE

The present invention is further described with reference to examples,but the invention is in no way limited to those examples.

The polyethylene resins used in Examples and Comparative Examples are asfollows.

Linear Polyethylene

(1) Ethylene-hexene-1 Copolymer (L-PE(1))

Catalyst used for preparation: Metallocene-type catalyst

Mw/Mn: 2.5

Density: 0.920 g/cm³

Melt flow rate: 1.0 g/10 min.

Content of component soluble in n-decane at room temperature: 0.2% byweight

Melt tension (MT): 3 g

(2) Ethylene-hexene-1 Copolymer (L-PE(2))

Catalyst used for preparation: Metallocene-type catalyst

Mw/Mn: 2.5

Density: 0.910 g/cm³

Melt flow rate: 0.5 g/10 min.

Content of component soluble in n-decane at room temperature: 0.1% byweight

Melt tension (MT): 6 g

(3) Ethylene-hexene-1 Copolymer (L-PE(3))

Catalyst used for preparation: Metallocene-type catalyst

Mw/MN: 2.8

Density: 0.950 g/cm³

Melt flow rate: 100 g/10 min.

Content of component soluble in n-decane at room temperature: 1.0% byweight

Melt tension (MT): 0.5 g

Physical properties of the aforesaid L-PE(1), L-PE(2), and L-PE (3),respectively, are shown in Table 1.

(4) Ethylene-hexene-1 Copolymer (L-PE(4))

Catalyst used for preparation: Ziegler-type catalyst

Mw/Mn: 5

Density: 0.925 g/cm³

Melt flow rate: 1.0 g/10 min.

Content of component soluble in n-decane at room temperature: 6.2% byweight

Melt tension (MT): 2 g

High-pressure Low-density Polyethylene (HPLDPE)

Density: 0.920 g/cm³

Melt flow rate: 0.5 g/10 min.

Content of component soluble in n-decane at room temperature: 0.3% byweight

Melt tension (MT): 15 g

Examples 1-4 and Comparative Examples 1-3

The polyethylene resins and polyethylene resin compounds shown in Table1 were tested as for their stress cracking resistance and adhesion ofprinting ink to the sheet in accordance with the aforesaid test methods.

By the way, said polyethylene resin compounds were prepared by means ofmixing and extruding those polyethylene components using a single-screwextruder (65 mm diameter) at a temperature of 200° C.

Test results are shown in Table 2 set forth as follows.

TABLE 1 Copolymers Kind L-PE (1) L-PE (2) L-PE (3) Comonom ContentHexene-1 Hexene-1 Hexene-1 er (mol %) 2.8 3.9 1.0 MFR(g/10 min.) 1.0 0.5100 Mw/Mn 2.5 2.5 2.8 Density (g/cm³) 0.920 0.910 0.950 Solubles inn-decane 0.2 0.1 0.1 (wt %) *1 1.57 4.08 — **1 — — 0.3 Tm (° C.) 115 112127 MT (g) 3 6 0.5 *2 2.2 3.9 0.05 *3 120 116 132 FI (s⁻¹) 420 280 12000*4 75 38 7500 *1: The value is equivalent to W < 80 × exp( −100(d −0.88)) + 0.1 **1: The value is equivalent to W < 80 × (MFR − 9)^(0.26) ×exp(−100(d − 0.88)) + 0.1 *2: The value is equivalent to 2.2 ×MFR^(−0.84) *3: The value is equivalent to 400 × d − 248 *4: The valueis equivalent to 75 × MFR

TABLE 2 Polyethylene resin Properties Solubles Polyethylene resincompound as a sheet MFR in n- MFR Solubles in ESCR Squared ratio (g/10Density MT decane (g/10 Density MT n-decane (hr) cut test Components (wt%) min) (g/cm³) (g) (wt %) min) (g/cm³) (g) (wt %) (*1) (*2) Example 1L-PE (1) 100 1.0 0.920 3 0.2 — — — — 300 100/100 Example 2 L-PE (2) 500.5 0.910 6 0.1 2.0 0.930 4 0.1 >600 100/100 L-PE (3) 50 100 0.950 0.50.1 Example 3 L-PE (1) 80 1.0 0.920 3 0.2 0.8 0.920 7 0.9 150 100/100HPLDPE 20 0.5 0.920 15 0.3 Example 4 L-PE (2) 40 0.5 0.910 6 0.1 1.50.926 8 0.1 500 100/100 L-PE (3) 40 100 0.950 0.5 0.1 HPLDPE 20 0.50.920 15 0.3 Comp. HPLDPE 100 0.5 0.920 15 0.3 — — — — 5 0/100 Example 1Comp. L-PE (4) 100 1.0 0.925 2 6.2 — — — — 150 15/100 Example 2 Comp.L-PE (4) 80 1.0 0.925 2 6.2 0.8 0.922 5 5.2 20 12/100 Example 3 HPLDPE20 0.5 0.920 15 0.3 (*1) 50% cracking appearance time (F₅₀)(environmental stress cracking resistance) (*2) The number of sectionswhich remained peel-free after the peeling test/100 (test sectionnumber)

Industrial Applicability

The present invention provides polyethylene resin and its compounds forcontainer uses, respectively, which realizes/realize molding ofthin-walled articles and high-speed molding, achieves/achieve excellentprintability and stress cracking resistance and is/are suitable forcontainer uses involving tubes, bottles, etc. and containers.

What is claimed is:
 1. A polyethylene resin for container uses whichcomprises linear polyethylene (A) satisfying the following requirements,(i) Molecular weight distribution (Mw/Mn) as determined by GPC is 2-3.5,(ii) Density is 0.890-0.975 g/cm³, and (iii) Content of componentsoluble in n-decane at room temperature is 2% by weight or less,achieves a 50% cracking appearance time (F50) of 100 hrs. or more, anddemonstrates that the printed surface as tested in a squared cut testperformed in the film form, does not substantially get peeled off. 2.The polyethylene resin for container uses according to claim 1 whereinsaid linear polyethylene (A) comprises linear polyethylene (A1)satisfying the following requirements; (i) Molecular weight distribution(Mw/Mn) as determined by GPC is 2-3.5, (ii) Density is 0.900-0.950g/cm³, and (iii) Content of component soluble in n-decane at roomtemperature is 2% by weight or less, and (iv) Melt flow rate is 0.1-10g/10 min.
 3. The polyethylene resin for container uses according toclaim 1 or claim 2 wherein said linear polyethylene (A) satisfies: (1)the following relationship between the melt tension (MT)(g) at atemperature of 190° C. and the melt flow rate (MFR) (g/10 min)MT>2.2×MFR^(−0.84) (2) the following relationship between the contentsoluble in decane (W)(% by weight) at room temperature and the density(d)(g/cm³); When MFR≦10 g/10 min, W<80×exp(−100(d−0.88))+0.1 When MFR>10g/10 min., W<80×(MFR−9)^(0.26)×exp(−100(d−0.88))+0.1; (3) the followingrelationship between a temperature of highest peak (Tm)(° C.) on theendothermic curve as determined using differential scanning calorimeter(DSC) and the density (d) Tm<400×d−248.
 4. The polyethylene resin forcontainer uses according to claim 3 wherein said linear polyethylene (A)furthermore satisfies 4) the following relationship between the fluidityindex (FI(1/sec)) as defined by the shear speed when the shear stress ofthe molten polymer at a temperature of 190° C. reaches 2.4×10⁶ dyne/cm²and the melt flow rate (MFR)(g/10 min.) FI>75×MFR.
 5. A containerobtained by molding the polyethylene resin defined in claim 1 or claim2.
 6. The container according to claim 5 wherein the molding is aextrusion blow molding.
 7. A polyethylene resin compound for containeruses which comprises linear polyethylene (A) satisfying the followingrequirements: (i) Molecular weight distribution (Mw/Mn) as determined byGPC is 2-3.5, (ii) Density is 0.890-0.975 g/cm³, and (iii) Content ofcomponent soluble in n-decane at room temperature is 2% by weight orless, achieves a 50% cracking appearance time (F₅₀) of 100 hrs. or more,and demonstrates that the printed surface as tested in a squared cuttest performed in the film form, does not substantially get peeled off.8. The polyethylene resin compound for container uses according to claim7 wherein the aforesaid linear polyethylene (A) satisfies the followingrequirements: (1) the following relationship between the melt tension(MT) (g) at a temperature of 190° C. and the melt flow rate (MFR)(g/10min.) MT>2.2×MFR^(−0.84) (2) the following relationship between thecontent of component soluble in decane at room temperature (W)(% byweight) and the density (d)(g/cm³); When MFR≦10 g/10 min.,W<80×exp(−100(d−0.88))+0.1 When MFR>10 g/10 min.,W<80×(MFR−9)^(0.26)×exp(−100(d−0.88))+0.1; (3) the followingrelationship between the temperature of highest peak (Tm)(° C.) in theendothermic curve as determined using differential scanning calorimeter(DSC) and the density (d) Tm<400d−248.
 9. The polyethylene resincompound for container uses according to claim 8 wherein the linearpolyethylene (A) furthermore satisfies (4) the following relationshipbetween the fluidity index (FI)(1/sec) which is defined by the shearrate when the shear stress of the molten polymer at a temperature of190° C. reaches 2.4×10⁶ dyne/cm² on one hand and the melt flow rate(MFR)(g/10 min.) on the other  FI>75×MFR.
 10. The polyethylene resincompound according to claim 7 which comprises more than 50% to less than100% by weight of linear polyethylene (A1) having a molecular weightdistribution (Mw/Mn) as determined by GPC of 2-3.5, a density of0.900-0.950 g/cm³, a content of component soluble in n-decane at roomtemperature of 2% by weight or less, and a melt flow rate of 0.1-10 g/10min., and not more than 50% to more than 0% by weight of high-pressurelow density polyethylene (B) having a density of 0.910-0.930 g/cm³ and amelt flow rate of 0.2-10 g/10 min.
 11. The polyethylene resin compoundfor container uses according to claim 7 which comprises at least 2components selected from the group consisting of 0-70% by weight oflinear polyethylene (A2) having a molecular weight distribution (Mw/Mn)as determined by GPC of 2-3.5, a density of 0.890-0.920 g/cm³, a contentof component soluble in n-decane at room temperature of 2% by weight orless, and a melt flow rate of 0.1-5 g/10 min.; 0-70% by weight of linearpolyethylene (A3) having a molecular weight distribution (Mw/Mn) asdetermined by GPC of 2-3.5, a density of 0.920-0.975 g/cm³, a content ofcomponent soluble in n-decane at room temperature of 2% by weight orless, and a melt flow rate of 5-300 g/10 min.; and 50-0% by weighthigh-pressure low-density polyethylene (B) having a density of0.910-0.930 g/cm³ and a melt flow rate of 0.2-10 g/10 min.
 12. Acontainer obtained by molding the polyethylene resin compound defined inany one of claims 7-11.
 13. The container according to claim 12 whereinthe molding is extrusion blow molding.
 14. A container obtained bymolding the polyethylene resin or the polyethylene resin compositiondefined in claim
 3. 15. The container according to claim 14, wherein themolding is an extrusion blow molding.
 16. The container according toclaim 14, which has a multi-layer construction of two or more layerswhose internal layer is formed from the polyethylene resin or thepolyethylene resin composition.